Ink including an organic material, display device using the same, and method of manufacturing display device

ABSTRACT

An ink for a display device, the ink includes: an organic material, wherein the organic material has a molecular weight greater than about 500 and less than about 1,000,000, and the organic material in the ink has a concentration and the molecular weight of the organic material satisfy:
 
 y&gt;− 3.518*1 n ( x )+45.59,
 
wherein y is the concentration of the organic material, and x is the molecular weight of the organic material.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit of Korean PatentApplication No. 10-2020-0071012, filed on Jun. 11, 2020, which is herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND Field

Exemplary implementations of the invention relate generally to a displaydevice and a method of manufacturing the display device, and moreparticularly, to an ink including an organic material, a display deviceusing the same, and a method of manufacturing the display device.

Discussion of the Background

With the development of the information society, the demand for displaydevices for displaying images has increased in various forms. In thefield of display devices, bulky cathode ray tubes (CRTs) have rapidlybeen replaced by thin, light, and large-sized flat-panel display (FPD)devices. Flat-panel displays may include liquid crystal displays (LCDs),plasma display panels (PDPs), organic light-emitting device (OLED)displays, electrophoretic display (EPD) devices, or the like.

Of the above display devices, an organic light-emitting display devicemay include, as a display element, an organic light-emitting diodeincluding an opposite electrode, a pixel electrode, and an emissionlayer. When a voltage is applied to the opposite electrode and the pixelelectrode of the organic light-emitting diode, the emission layer mayemit visible light. An intermediate layer of the organic light-emittingdiode may be formed by discharging ink containing an organic materialonto the pixel electrode.

The above information disclosed in this Background section is only forunderstanding of the background of the inventive concepts, and,therefore, it may contain information that does not constitute priorart.

SUMMARY

Applicant discovered that, in a display device according to the relatedart, when the molecular weight of an organic material forming theintermediate layer is low, adjacent pixels are contaminated in heatingprocesses during manufacture.

An ink including an organic material, a display device using the same,and a method of manufacturing display device according to principles andexemplary implementations of the invention are capable of improvingreliability of the display device and simultaneously increasingefficiency during manufacturing, by specific physical properties oforganic material in the ink that may be obtained, for example, bycorrelating the viscosity of ink, the concentration of ink, and themolecular weight of the organic material contained in the ink, to deducethe relationship between the concentration of ink and the molecularweight of the organic material that produce technical benefits such ashigh resolution and reduction or elimination of contamination betweenadjacent pixels.

Additional features of the inventive concepts will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the inventive concepts.

According to one aspect of the invention, an ink for a display device,the ink includes: an organic material, wherein the organic material hasa molecular weight greater than about 500 and less than about 1,000,000,and the organic material in the ink has a concentration and themolecular weight of the organic material satisfy:y>−3.518*ln(x)+45.59,

wherein y is the concentration of the organic material, and x is themolecular weight of the organic material.

The molecular weight of the organic material may be greater than about500 and less than about 400,000.

The ink may have an Ohnesorge number of less than about 1.

The viscosity of the ink may be less than or equal to about 25 cP.

According to another aspect of the invention, a display device includes:a substrate; a pixel electrode disposed on the substrate; a bank layerdisposed on the pixel electrode, the bank layer including an openingexposing at least part of the pixel electrode; and an intermediate layeroverlapping the opening and including an organic material, wherein theintermediate layer is disposed on the pixel electrode at least partiallyexposed by the bank layer, the organic material has a molecular weightgreater than about 500 and less than about 1,000,000, and the organicmaterial comprises ink having a concentration and the molecular weightof the organic material satisfy:y>−3.518*ln(x)+45.59,

wherein y is the concentration of the organic material, and x is themolecular weight of the organic material.

The molecular weight of the organic material may be greater than about500 and less than about 400,000.

The ink may have an Ohnesorge number of less than about 1.

The viscosity of the ink may be less than or equal to about 25 cP.

An upper surface of the bank layer may have liquid repellency.

An upper surface and a lateral surface of the bank layer may have liquidrepellency.

The bank layer may include a fluorine resin.

The bank layer may include a negative photoresist.

The intermediate layer may be disposed in an opening of the bank layer.

An opposite electrode may be disposed on the intermediate layer.

The opposite electrode may cover the intermediate layer and the banklayer.

According to a further aspect of the invention, a method ofmanufacturing a display device, the method including the steps of:forming a pixel electrode on a substrate; forming a bank layer on thepixel electrode, the bank layer having an opening exposing at least partof the pixel electrode; and forming an intermediate layer on the pixelelectrode by discharging ink comprising an organic material onto thepixel electrode, wherein the organic material has a molecular weightgreater than about 500 and less than about 1,000,000, and the organicmaterial in the ink has a concentration and the molecular weight of theorganic material satisfy:y>−3.518*ln(x)+45.59,

wherein y is the concentration of the organic material, and x is themolecular weight of the organic material.

The molecular weight of the organic material may be greater than about500 and less than about 400,000.

The ink may have an Ohnesorge number of less than about 1.

The viscosity of the ink may be less than or equal to about 25 cP.

The step of forming the bank layer may include: forming a photoresistlayer on the pixel electrode; exposing at least part of the photoresistlayer; and forming the bank layer by at least partially exposing thephotoresist layer.

The opening of the bank layer may be formed by developing thephotoresist layer.

The intermediate layer may be disposed in the opening of the bank layer.

After the forming of the bank layer, the step of heating the bank layermay be conducted.

An upper surface of the bank layer may have liquid repellency.

An upper surface and a lateral surface of the bank layer may have liquidrepellency.

The bank layer may include a fluorine resin.

The bank layer may include a negative photoresist.

After the forming of the intermediate layer, the step of forming anopposite electrode on the intermediate layer may be conducted.

The opposite electrode may cover the intermediate layer and the banklayer.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate exemplary embodiments of theinvention, and together with the description serve to explain theinventive concepts.

FIG. 1 is a schematic perspective view illustrating an exemplaryembodiment of a display device constructed according to principles ofthe invention.

FIG. 2 is a schematic cross-sectional view of the display device takenalong a line I-I′ of FIG. 1 .

FIGS. 3 to 8 are cross-sectional views schematically illustrating anexemplary embodiment of a process of manufacturing a display deviceaccording to principles of the invention.

FIG. 9 is a graphical depiction of some comparative and exemplaryembodiments comparing viscosity with concentration of ink for eachmolecular weight.

FIG. 10 is a graphical depiction of some exemplary embodiments comparingmolecular weight versus concentration when the viscosity of ink is lessthan or equal to about 25 cP according to principles of the invention.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of various exemplary embodiments or implementations of theinvention. As used herein “embodiments” and “implementations” areinterchangeable words that are non-limiting examples of devices ormethods employing one or more of the inventive concepts disclosedherein. It is apparent, however, that various exemplary embodiments maybe practiced without these specific details or with one or moreequivalent arrangements. In other instances, well-known structures anddevices are shown in block diagram form in order to avoid unnecessarilyobscuring various exemplary embodiments. Further, various exemplaryembodiments may be different, but do not have to be exclusive. Forexample, specific shapes, configurations, and characteristics of anexemplary embodiment may be used or implemented in another exemplaryembodiment without departing from the inventive concepts.

Unless otherwise specified, the illustrated exemplary embodiments are tobe understood as providing exemplary features of varying detail of someways in which the inventive concepts may be implemented in practice.Therefore, unless otherwise specified, the features, components,modules, layers, films, panels, regions, plates, and/or aspects, etc.(hereinafter individually or collectively referred to as “elements”), ofthe various embodiments may be otherwise combined, separated,interchanged, and/or rearranged without departing from the inventiveconcepts.

The use of cross-hatching and/or shading in the accompanying drawings isgenerally provided to clarify boundaries between adjacent elements. Assuch, neither the presence nor the absence of cross-hatching or shadingconveys or indicates any preference or requirement for particularmaterials, material properties, dimensions, proportions, commonalitiesbetween illustrated elements, and/or any other characteristic,attribute, property, etc., of the elements, unless specified. Further,in the accompanying drawings, the size and relative sizes of elementsmay be exaggerated for clarity and/or descriptive purposes. When anexemplary embodiment may be implemented differently, a specific processorder may be performed differently from the described order. Forexample, two consecutively described processes may be performedsubstantially at the same time or performed in an order opposite to thedescribed order. Also, like reference numerals denote like elements.

When an element, such as a layer, is referred to as being “on,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, connected to, or coupled to the other element or layer orintervening elements or layers may be present. When, however, an elementor layer is referred to as being “directly on,” “directly connected to,”or “directly coupled to” another element or layer, there are nointervening elements or layers present. To this end, the term“connected” may refer to physical, electrical, and/or fluid connection,with or without intervening elements. Further, the D1-axis, the D2-axis,and the D3-axis are not limited to three axes of a rectangularcoordinate system, such as the x, y, and z-axes, and may be interpretedin a broader sense. For example, the D1-axis, the D2-axis, and theD3-axis may be perpendicular to one another, or may represent differentdirections that are not perpendicular to one another. For the purposesof this disclosure, “at least one of X, Y, and Z” and “at least oneselected from the group consisting of X, Y, and Z” may be construed as Xonly, Y only, Z only, or any combination of two or more of X, Y, and Z,such as, for instance, XYZ, XYY, YZ, and ZZ. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items. Furthermore, the expression such as “at leastone of A and B” may include A, B, or A and B.

Although the terms “first,” “second,” etc. may be used herein todescribe various types of elements, these elements should not be limitedby these terms. These terms are used to distinguish one element fromanother element. Thus, a first element discussed below could be termed asecond element without departing from the teachings of the disclosure.

Spatially relative terms, such as “beneath,” “below,” “under,” “lower,”“above,” “upper,” “over,” “higher,” “side” (e.g., as in “sidewall”), andthe like, may be used herein for descriptive purposes, and, thereby, todescribe one elements relationship to another element(s) as illustratedin the drawings. Spatially relative terms are intended to encompassdifferent orientations of an apparatus in use, operation, and/ormanufacture in addition to the orientation depicted in the drawings. Forexample, if the apparatus in the drawings is turned over, elementsdescribed as “below” or “beneath” other elements or features would thenbe oriented “above” the other elements or features. Thus, the exemplaryterm “below” can encompass both an orientation of above and below.Furthermore, the apparatus may be otherwise oriented (e.g., rotated 90degrees or at other orientations), and, as such, the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting. As used herein, thesingular forms, “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. Moreover,the terms “comprises,” “comprising,” “includes,” and/or “including,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, components, and/orgroups thereof, but do not preclude the presence or addition of one ormore other features, integers, steps, operations, elements, components,and/or groups thereof. It is also noted that, as used herein, the terms“substantially,” “about,” and other similar terms, are used as terms ofapproximation and not as terms of degree, and, as such, are utilized toaccount for inherent deviations in measured, calculated, and/or providedvalues that would be recognized by one of ordinary skill in the art.

As an example, the meaning that the wiring “extends in the firstdirection or the second direction” includes not only extending in agenerally linear shape, but also extending generally in a zigzag or acurve along the first direction or the second direction.

Various exemplary embodiments are described herein with reference tosectional and/or exploded illustrations that are schematic illustrationsof idealized exemplary embodiments and/or intermediate structures. Assuch, variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, exemplary embodiments disclosed herein should notnecessarily be construed as limited to the particular illustrated shapesof regions, but are to include deviations in shapes that result from,for instance, manufacturing. In this manner, regions illustrated in thedrawings may be schematic in nature and the shapes of these regions maynot reflect actual shapes of regions of a device and, as such, are notnecessarily intended to be limiting. Moreover, when referred to as “on aplane” or “on a plan view,” this may mean when an object part is viewedfrom above, and it may be referred to as “in a cross-section,” when theobject part is cut vertically and viewed from the side. Also, whenreferred to as “overlapping,” it may include overlapping “on a plane,”“on a plan view,” and “in a cross-section.”

As used herein, the term “concentration” can mean the amount of a givensubstance in a state unit or mixture, solution, or ore and have a weightbasis.

As used herein, the term “molecular weights” can mean “weight averagemolecular weight” or “number average molecular weight”.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure is a part. Terms,such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and should not be interpreted in anidealized or overly formal sense, unless expressly so defined herein.

As described herein, irrelevant portions to the description are omitted,and in the description with reference to the drawings, the same orcorresponding constituents are indicated by the same reference numeralsand redundant descriptions thereof are omitted.

FIG. 1 is a schematic perspective view illustrating an exemplaryembodiment of a display device constructed according to principles ofthe invention.

Referring to FIG. 1 , the display device 1 may include a display area DAand a non-display area NDA disposed around the display area DA. Thenon-display area NDA may surround the display area DA. The displaydevice 1 may provide an image by using light emitted from a plurality ofpixels P disposed in the display area DA, and the non-display area NDAmay be an area where no image is displayed.

In the following description, although an organic light-emitting displaydevice is described as an example of the display device 1, exemplaryembodiments are not limited thereto. In some exemplary embodiments, thedisplay device 1 may include a display device such as an inorganiclight-emitting display device, an inorganic display device, or a quantumdot light-emitting display device. For example, the emission layer of adisplay element provided in the display device 1 may include an organicmaterial, an inorganic material, a quantum dot, an organic material anda quantum dot, or an inorganic material and a quantum dot.

Although FIG. 1 illustrates the display device 1 having a generally flatdisplay surface, but the exemplary embodiments are not limited thereto.In some embodiments, the display device 1 may include athree-dimensional display surface or a generally curved display surface.

When the display device 1 includes a three-dimensional display surface,the display device 1 may include a plurality of display areas indicatingdifferent directions, for example, a generally polygonal column typedisplay surface. In some exemplary embodiments, when the display device1 includes a generally curved display surface, the display device 1 maybe embodied in various forms including flexible, foldable, and rollabledisplay devices.

FIG. 1 illustrates the display device 1 in the form of a mobile phoneterminal. The display device also may be in the form of electronicmodules, such as a camera module, a power module, or the like, which aremounted on a main board, are disposed in the bracket/case together withthe display device 1. In particular, the display device 1 may be in theform of small and medium-sized electronic devices such as tablets, carnavigation devices, game machines, smart watches, or the like, as wellas large electronic devices such as televisions and monitors.

Although FIG. 1 illustrates a case in which the display area DA of thedisplay device 1 is generally rectangular, the shape of the display areaDA may be generally circular, generally oval, or generally polygonalsuch as generally triangular or generally pentagonal.

The display device 1 may include the pixels P disposed in the displayarea DA. Each of the pixels P may include an organic light-emittingdiode (OLED). Each of the pixels P may emit light of, for example, ared, green, blue, or white color through the OLED. In some exemplaryembodiments, the representative pixel P may be a pixel that emits lightof any one color of red, green, blue, or white, as described above.

FIG. 2 is a schematic cross-sectional view of the display device takenalong a line I-I′ of FIG. 1 .

Referring to FIG. 2 , the display device 1 may include a substrate 100and the OLED disposed on the substrate 100. In the followingdescription, detailed descriptions are presented in a stacking order ofthe display device 1 according to some exemplary embodiments.

The substrate 100 may include a glass material, a ceramic material, ametal material, or a material having flexible or bendablecharacteristics. When the substrate 100 has flexible or bendablecharacteristics, the substrate 100 may include a polymer resin such as apolyethersulfone, a polyacrylate, a polyetherimide, a polyethylenenaphthalate, a polyethylene terephthalate, a polyphenylene sulfide, apolyarylate, polyimide, a polycarbonate, or a cellulose acetatepropionate. The substrate 100 may have a single layer or a multilayerstructure of the above material, and for a multilayer structure, aninorganic layer may be further included. In some exemplary embodiments,the substrate 100 may have a structure of an organic material/aninorganic material/an organic material.

A buffer layer 107 may be disposed on the substrate 100. The bufferlayer 107 is located on the substrate 100 to reduce or prevent intrusionof foreign materials, moisture, or external air from the bottom of thesubstrate 100, and may provide a planarized surface on the substrate100. The buffer layer 107 may include an inorganic material such as anoxide or a nitride, an organic material, or an organic/inorganiccomposite, and may have a single layer or a multilayer structure of aninorganic material and an organic material.

A barrier layer may be further provided between the substrate 100 andthe buffer layer 107. The barrier layer may prevent or reduce intrusionof impurities from the substrate 100 or the like into a semiconductorlayer 134 that is described below. The barrier layer may include aninorganic material such as an oxide or a nitride, an organic material,or an organic/inorganic composite, and may have a single layer or amultilayer structure of an inorganic material and an organic material.

A thin film transistor TFT may be disposed on the buffer layer 107. TheTFT may include the semiconductor layer 134, a gate electrode 136overlapping the semiconductor layer 134, and connection electrodeselectrically connected to the semiconductor layer 134. The TFT isconnected to the OLED to drive the OLED.

The semiconductor layer 134 is disposed on the buffer layer 107, and mayinclude a channel region 131 overlapping with the gate electrode 136,and a source region 132 and a drain region 133 disposed at both sides ofthe channel region 131 and including impurities of a concentrationhigher than that of the channel region 131. The impurities may include aN-type impurities or a P-type impurities. The source region 132 and thedrain region 133 may be electrically connected to the connectionelectrodes.

The semiconductor layer 134 may include an oxide semiconductor and/or asilicon semiconductor. When the semiconductor layer 134 includes anoxide semiconductor, for example, an oxide of at least one materialselected from the group consisting of indium (In), gallium (Ga), tin(Sn), zirconium (Zr), vanadium (V), hafnium (Hf), cadmium (Cd),germanium (Ge), chromium (Cr), titanium (Ti), and zinc (Zn). Forexample, the semiconductor layer 134 may include ITZO (InSnZnO), IGZO(InGaZnO), or the like. When the semiconductor layer 134 includes asilicon semiconductor, for example, an amorphous silicon (a-Si) or a lowtemperature polysilicon (LTPS) obtained by crystallizing the amorphoussilicon (a-Si).

A first insulating layer 109 may be disposed on the semiconductor layer134. The first insulating layer 109 may include at least one inorganicinsulating material selected from the group consisting of silicon oxide(SiO₂), a silicon nitride (SiN_(x)), silicon oxynitride (SiON), aluminumoxide (Al₂O₃), titanium oxide (TiO₂), tantalum oxide (Ta₂O₅), hafniumoxide (HfO₂), and zinc oxide (ZnO₂). The first insulating layer 109 maybe a single layer or a multilayer including the above-describedinorganic insulating material.

The gate electrode 136 may be disposed on the first insulating layer109. The gate electrode 136 may be formed in a single layer or amultilayer including at least one metal material selected from the groupconsisting of aluminum (Al), platinum (Pt), palladium (Pd), silver (Ag),magnesium (Mg), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir),chromium (Cr), lithium (Li), calcium (Ca), molybdenum (Mo), titanium(Ti), tungsten (W), and copper (Cu). The gate electrode 136 may beconnected to a gate line for applying an electrical signal to the gateelectrode 136.

A second insulating layer 111 may be disposed on the gate electrode 136.The second insulating layer 111 may include at least one inorganicinsulating material selected from the group consisting of SiO₂, aSiN_(x), SiON, Al₂O₃, TiO₂, Ta₂O₅, HfO₂, and ZnO₂. The second insulatinglayer 111 may be a single layer or a multilayer including theabove-described inorganic insulating material.

A storage capacitor Cst may be disposed on the first insulating layer109. The storage capacitor Cst may include a lower electrode 144 and anupper electrode 146 overlapping with the lower electrode 144. The lowerelectrode 144 and the upper electrode 146 of the storage capacitor Cstmay overlap with each other with the second insulating layer 111therebetween.

In some exemplary embodiments, the lower electrode 144 of the storagecapacitor Cst overlaps with the gate electrode 136 of the TFT, and thelower electrode 144 of the storage capacitor Cst may be providedintegrally with the gate electrode 136 of the TFT. In another exemplaryembodiment, the lower electrode 144 of the storage capacitor Cst doesnot overlap with the gate electrode 136 of the TFT, and may be disposed,as a separate independent constituent element, on the first insulatinglayer 109 or the second insulating layer 111.

The upper electrode 146 of the storage capacitor Cst may include Al, Pt,Pd, Ag, Mg, Au, Ni, Nd, Ir, Cr, Li, Ca, Mo, Ti, W, and/or Cu, and may bea single layer or a multilayer of the above-described material.

A third insulating layer 113 may be disposed on the upper electrode 146of the storage capacitor Cst. The third insulating layer 113 may includeat least one inorganic insulating material selected from the groupconsisting of SiO₂, a SiN_(x), SiON, Al₂O₃, TiO₂, Ta₂O₅, HfO₂, and ZnO₂.The third insulating layer 113 may be a single layer or a multilayerincluding the above-described inorganic insulating material.

A source electrode 137 and a drain electrode 138, which are theconnection electrodes, may be disposed on the third insulating layer113. The source electrode 137 and the drain electrode 138 may include aconductive material including Mo, Al, Cu, Ti, or the like, and may beformed in a single layer or a multilayer including the above materials.The source electrode 137 and the drain electrode 138 may have amultilayer structure of Ti/Al/Ti.

A first planarization layer 117 may be disposed on the source electrode137 and the drain electrode 138. The first planarization layer 117 maybe formed in a single layer or a multilayer of a film including anorganic material or an inorganic material. In some exemplaryembodiments, the first planarization layer 117 may include generalpurpose polymers such as benzocyclobutene (BCB), polyimide (PI),hexamethyldisiloxane (HMDSO), polymethylmethacrylate (PMMA), andpolystyrene (PS), polymer derivatives with phenolic groups, acrylicpolymers, imide polymers, aryl ether polymers, amide polymers, fluorinepolymers, p-xylene polymers, vinyl alcohol polymers, blends thereof, orthe like. The first planarization layer 117 may include SiO₂, a SiN_(x),SiON, Al₂O₃, TiO₂, Ta₂O₅, HfO₂, ZnO₂, or the like. After the firstplanarization layer 117 is formed, chemical mechanical polishing may beperformed to provide a planarized upper surface.

A contact metal layer CM may be disposed on the first planarizationlayer 117. The contact metal layer CM may include Al, Cu, Ti, or thelike, and may be formed in a single layer or a multilayer. The contactmetal layer CM may have a multilayer structure of Ti/Al/Ti.

A second planarization layer 119 may be disposed on the contact metallayer CM. The second planarization layer 119 may be formed in a singlelayer or a multilayer of a film including an organic material or aninorganic material. In some exemplary embodiments, the secondplanarization layer 119 may include the same material as that of thefirst planarization layer 117. In another exemplary embodiment, thesecond planarization layer 119 may include a material different fromthat of the first planarization layer 117. After the secondplanarization layer 119 is formed, chemical mechanical polishing may beperformed to provide a planarized upper surface. In some exemplaryembodiments, the second planarization layer 119 may be omitted.

The OLED including a pixel electrode 210, an intermediate layer 220, andan opposite electrode 230 may be disposed on the second planarizationlayer 119. The pixel electrode 210 may be electrically connected to thecontact metal layer CM via a contact hole penetrating the secondplanarization layer 119, and the contact metal layer CM may beelectrically connected to the source electrode 137 or the drainelectrode 138, which are the connection electrodes of the TFT, via acontact hole penetrating the first planarization layer 117, so that theOLED may be electrically connected to the TFT.

The pixel electrode 210 may be disposed on the second planarizationlayer 119. The pixel electrode 210 may be a (semi-)transmissiveelectrode or a reflective electrode. The pixel electrode 210 may includea reflective film including Al, Pt, Pd, Ag, Mg, Au, Ni, Nd, Ir, Cr, Li,Ca, Mo, Ti, W, Cu, a compound thereof, or the like, and a transparent orsemi-transparent electrode layer formed on the reflective film. Thetransparent or semi-transparent electrode layer may include at least oneselected from the group consisting of an indium tin oxide (ITO), anindium zinc oxide (IZO), ZnO, indium oxide (In₂O₃), an indium galliumoxide (IGO), and an aluminum zinc oxide (AZO). The pixel electrode 210may have a stack structure of ITO/Ag/ITO.

A bank layer 180 may be disposed on the second planarization layer 119,and the bank layer 180 may have an opening OP that exposes at least partof the pixel electrode 210. An area exposed by the opening OP of thebank layer 180 may be defined to be an emission area EA. The peripheryof the emission area EA forms a non-emission area NEA, and thenon-emission area NEA may surround the emission areas EA. In otherwords, the display area DA may include the emission areas EA and thenon-emission area NEA surrounding the emission areas EA. The bank layer180 may prevent generation of an arc or the like at an edge of the pixelelectrode 210 by increasing the distance between the opposite electrodes230 above the pixel electrode 210. The bank layer 180 may include anorganic insulating material such as a polyimide, a polyamide, an acrylicresin, a benzocyclobutene, a hexamethyldisiloxane (HMDSO), a phenolresin, or the like.

In some exemplary embodiments, the bank layer 180 may include aphotoresist, that is, a photosensitive resin. In detail, the bank layer180 may include a negative photoresist. For example, the bank layer 180may include an epoxy-based polymer or an off-stoichiometry thiol-enes(OSTE) polymer. In another exemplary embodiment, the bank layer 180 mayinclude a positive photoresist.

The bank layer 180 may have liquid repellency. In some exemplaryembodiments, an upper surface 180 a of the bank layer 180 may haveliquid repellency. In some exemplary embodiments, having liquidrepellency may mean that, during an inkjet process, a contact angle withrespect to a solvent constituting the ink including the organic materialfor forming the intermediate layer 220 that is described below, or withrespect to the ink including an organic material, is greater than orequal to about 90°. In other words, having liquid repellency may meansthat, during an inkjet process, the contact angle with respect to asolvent constituting the ink including the organic material for formingthe intermediate layer 220, or with respect to the ink including anorganic material, is relatively large. As the upper surface 180 a of thebank layer 180 has liquid repellency, during an inkjet process, thenon-emission area NEA may be prevented or reduced from being coated withink including an organic material. In another exemplary embodiment, notonly the upper surface 180 a of the bank layer 180, but also a lateralsurface 180 b of the bank layer 180 may have liquid repellency.

The bank layer 180 may include a fluorine resin. For example, the banklayer 180 may include an organic material having unsaturated bonding anda fluoro group. Alternatively, the bank layer 180 may include an organicmaterial having unsaturated bonding and fluorine. The fluoro group orfluorine included in a surface of the bank layer 180 may improve liquidrepellency of the upper surface 180 a of the bank layer 180.

The intermediate layer 220 may be disposed on the pixel electrode 210that is at least partially exposed by the bank layer 180. In otherwords, the intermediate layer 220 may be disposed in the opening OPdefined in the bank layer 180. In some exemplary embodiments, theintermediate layer 220 may include an emission layer, a first functionallayer and a second functional layer may be respectively disposed underand above the emission layer. The first functional layer, which is aconstituent element disposed under the emission layer, may include ahole transport layer, or a hole transport layer and a hole injectionlayer. The second functional layer, which is a constituent elementdisposed above the emission layer, may include an electron transportlayer, or an electron transport layer and an electron injection layer.The first functional layer and the second functional layer may beoptionally respectively disposed under and above the emission layer.

The emission layer may include an organic material including afluorescent or phosphorescent material emitting red, green, blue, orwhite light. The emission layer may include a low molecular organicmaterial or a polymer organic material.

When the emission layer includes a low molecular organic material,layers of a hole injection layer, a hole transport layer, an electrontransport layer, an electron injection layer, or the like may bedisposed above and under the emission layer, and the emission layer mayinclude, as the low molecular organic material, various organicmaterials such as copper phthalocyanine (CuPc),N,N′-Di(napthalene-1-yl)-N,N′-diphenyl-benzidine (NPB),tris-8-hydroxyquinoline aluminum (Alq3), or the like.

When the emission layer includes a polymer organic material, the holetransport layer may be disposed above or under the emission layer. Inthis state, the hole transport layer may includepoly(3,4-ethylenedioxythiophene) PEDOT, and the emission layer mayinclude a poly-phenylene vinylene (PPV) based polymer material, apolyfluorene based polymer material, or the like.

The intermediate layer 220 included in the display device 1 according tosome exemplary embodiments may be formed in an inkjet printing process.In detail, the intermediate layer 220 according to some exemplaryembodiments may be formed by discharging ink 450 containing an organicmaterial (see FIG. 7 ) onto the pixel electrode 210. The ink 450containing an organic material for forming the intermediate layer 220 isdescribed in detail in the method of manufacturing a display device.

The opposite electrode 230 may be disposed on the intermediate layer220. The opposite electrode 230 may be disposed on the intermediatelayer 220 in a manner covering substantially the entirety of theintermediate layer 220. The opposite electrode 230 may be disposed abovethe display area DA in a manner covering substantially the entirety ofthe display area DA. In other words, the opposite electrode 230 may beintegrally formed in the entirety of the display area DA to cover thepixels P disposed in the display area DA by using an open mask.

The opposite electrode 230 may include a conductive material having alow work function. For example, the opposite electrode 230 may include a(semi-)transparent layer including Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir,Cr, Li, Ca, or an alloy thereof, or the like. Alternatively, theopposite electrode 230 may further include a layer such as ITO, IZO,ZnO, or In₂O₃ on the (semi-)transparent layer including theabove-described material.

The OLED may be covered by a thin film encapsulation layer. The thinfilm encapsulation layer may include at least one inorganicencapsulation layer and at least one organic encapsulation layer. TheOLED may be covered by an encapsulation plate.

FIGS. 3 to 8 are cross-sectional views schematically illustrating anexemplary embodiment of a process of manufacturing a display deviceaccording to principles of the invention.

A method of manufacturing the display device 1 according to someexemplary embodiments is described in order with reference to FIGS. 3 to8 . Referring to FIGS. 3 to 8 , the method of manufacturing the displaydevice 1 according to some exemplary embodiments may include forming thepixel electrode 210 on the substrate 100, forming, on the pixelelectrode 210, the bank layer 180 including the opening OP that exposesat least part of the pixel electrode 210, and forming the intermediatelayer 220 by discharging the ink 450 containing an organic material ontothe pixel electrode 210.

Furthermore, the method of manufacturing the display device 1 accordingto some exemplary embodiments may further include, after the forming ofthe intermediate layer 220 by discharging the ink 450 containing anorganic material onto the pixel electrode 210, forming the oppositeelectrode 230 on the intermediate layer 220.

First, the TFT may be formed on the substrate 100. The TFT may includethe semiconductor layer 134, the gate electrode 136, the sourceelectrode 137, and the drain electrode 138. Furthermore, the bufferlayer 107 may be formed on the substrate 100, and the first insulatinglayer 109, the second insulating layer 111, the third insulating layer113, the first planarization layer 117, and the second planarizationlayer 119 may be sequentially formed on and above the buffer layer 107.For example, at least part of the first insulating layer 109, the secondinsulating layer 111, the third insulating layer 113, the firstplanarization layer 117, and the second planarization layer 119 may beomitted.

Referring to FIG. 3 , the pixel electrode 210 may be formed on thesecond planarization layer 119. In some exemplary embodiments, the pixelelectrode 210 may have a stacking structure of ITO/Ag/ITO.

After the forming of the pixel electrode 210 on the substrate 100, theforming of, the bank layer 180 on the pixel electrode 210, including theopening OP that exposes at least part of the pixel electrode 210, may befurther performed.

In some exemplary embodiments, the forming of, on the pixel electrode210, the bank layer 180 including the opening OP that exposes at leastpart of the pixel electrode 210 may include forming a photoresist layer180M on the pixel electrode 210, exposing at least part of thephotoresist layer 180M, forming the bank layer 180 by developing thephotoresist layer 180M that is at least partially exposed, and heatingthe bank layer 180.

Referring to FIG. 4 , after the forming of the pixel electrode 210 onthe substrate 100, the forming of the photoresist layer 180M on thepixel electrode 210 may be performed.

The photoresist layer 180M may include photosensitive resin. Forexample, the photoresist layer 180M may include a negative photoresist.The photoresist layer 180M may include an organic insulating materialsuch as a polyimide, a polyamide, an acrylic resin, a benzocyclobutene,an HMDSO, a phenol resin, or the like. Furthermore, the photoresistlayer 180M may include an epoxy-based polymer or an off-stoichiometrythiol-enes (OSTE) polymer. In another exemplary embodiment, thephotoresist layer 180M may include a positive photoresist.

The photoresist layer 180M may include a fluorine resin. For example,the photoresist layer 180M may include an organic material and a fluorogroup having unsaturated bonding. Alternatively, the photoresist layer180M may include an organic material and a fluorine having unsaturatedbonding.

Referring to FIG. 5 , after the forming of the photoresist layer 180M onthe pixel electrode 210, exposing of at least part of the photoresistlayer 180M may be performed. In the step of exposing of at least part ofthe photoresist layer 180M, at least part of the photoresist layer 180Mmay be exposed by using a mask 500 including a light shielding portion501 and a light transmitting portion 502.

While a part of the photoresist layer 180M that overlaps with the lighttransmitting portion 502 of the mask 500 may be exposed, the rest of thephotoresist layer 180M that overlaps with the light shielding portion501 of the mask 500 may not be exposed.

Referring to FIG. 6 , after the exposing of the at least part of thephotoresist layer 180M, the step of forming of the bank layer 180 bydeveloping the photoresist layer 180M that is at least partially exposedmay be performed.

In some exemplary embodiments, when the photoresist layer 180M include anegative photoresist, a portion overlapping with the light transmittingportion 502 of the mask 500 may be formed as the bank layer 180, and aportion overlapping with the light shielding portion 501 of the mask 500may be formed as the opening OP. In another exemplary embodiment, whenthe photoresist layer 180M includes a positive photoresist, the portionoverlapping with the light transmitting portion 502 of the mask 500 maybe formed as the opening OP. The portion overlapping with the lightshielding portion 501 of the mask 500 may be formed as the bank layer180.

After the forming of the bank layer 180 by developing the photoresistlayer 180M that is at least partially exposed, the step of heating ofthe bank layer 180 may be performed. During the heating of the banklayer 180, a liquid repellent material or a hydrophobic materialincluded in the bank layer 180 may rise to be the upper surface 180 a ofthe bank layer 180. Accordingly, the upper surface 180 a of the banklayer 180 may have liquid repellency, and the lateral surface 180 b ofthe bank layer 180 may not have liquid repellency. In another exemplaryembodiment, not only the upper surface 180 a of the bank layer 180, butalso the lateral surface 180 b of the bank layer 180, may have liquidrepellency.

The bank layer 180 may include a fluorine resin. For example, the banklayer 180 may include an organic material and a fluoro group havingunsaturated bonding. Alternatively, the bank layer 180 may include anorganic material and a fluorine having unsaturated bonding. The fluorogroup or fluorine included in the surface of the bank layer 180 mayimprove liquid repellency of the upper surface 180 a of the bank layer180.

Referring to FIG. 7 , after the step of forming of the bank layer 180,on the pixel electrode 210, including the opening OP that exposes atleast part of the pixel electrode 210, the step of forming of theintermediate layer 220 by discharging the ink 450 containing an organicmaterial onto the pixel electrode 210 may be performed.

The intermediate layer 220 according to some exemplary embodiments maybe formed through an inkjet printing process. In detail, as the ink 450containing an organic material is discharged from an ink dischargeportion 400 including a nozzle 410 onto the pixel electrode 210, theintermediate layer 220 may be formed.

The ink 450 discharged from the ink discharge portion 400 may include anorganic material. The molecular weight of the organic material containedin the ink 450 may have a range of greater than about 500 and less thanabout 1,000,000, and various modifications are possible, for example,the molecular weight of the organic material contained in the ink 450may have a range of greater than about 500 and less than about 400,000,a range of greater than about 500 and less than about 300,000, or thelike.

For example, when the molecular weight of the organic material containedin the ink 450 is less than about 500, a problem may occur duringheating in that the organic material spreads to adjacent pixels tocontaminate the adjacent pixels. Furthermore, when the molecular weightof the organic material contained in the ink 450 is high, the viscosityof the ink 450 increases so that it may be difficult to adjust theamount of the ink 450 discharged from the ink discharge portion 400.Accordingly, when the molecular weight of the organic material containedin the ink 450 has a range of greater than about 500 and less than about1,000,000, the contamination of adjacent pixels due to the organicmaterial spreads to the adjacent pixels may be substantially reduced orprevented, and as the amount of the ink 450 discharged from the inkdischarge portion 400 is efficiently controlled, the display device 1may have a high resolution.

To produce a display device 1 of a high resolution, the amount of theink 450 discharged from the ink discharge portion 400 is reduced, andthe concentration of the ink 450 is increased. However, when theconcentration of the ink 450 is increased, the viscosity of the ink 450increases so that it is difficult to reduce the discharge amount of theink 450.

An Ohnesorge number Oh is used as a dimensionless number of fluidproperties to solve the fluid's Navier-stokes equation and establish afluid dynamics model for the inkjet printing process. The Ohnesorgenumber Oh is defined as in Mathematical Formula 1 below

$\begin{matrix}{{Oh} = \frac{\eta}{\sqrt{{\rho\sigma}\; d}}} & {\text{<}{Mathematical}\mspace{14mu}{Formula}\mspace{14mu} 1\text{>}}\end{matrix}$

where η denotes viscosity, ρ denotes density, σ denotes surface tension,and d denotes the diameter of a nozzle.

In general, when the Ohnesorge number Oh of ink used for a drop ondemand (DOD) type inkjet printing process is great, as the viscosity ofink serves as a dominant factor, a large pressure is needed fordischarging the ink, the speed of ink decreases, and the tail of the inkis elongated, so that the resolution of a display device maydeteriorate. In some exemplary embodiments, to produce a display device1 having a high resolution, the Ohnesorge number Oh of the ink 450containing an organic material may be less than about 1. To produce adisplay device 1 having a high resolution, ink is discharged under about3 picoliter (pL), and the maximum viscosity that is dischargeable atabout 3 pL may be induced as follows.

Assuming that, at a temperature of about 15° C. to about 50° C., thedensity of the ink containing an organic material is about 0.99 g/cm³,surface tension is about 34.5 mN/m, and the diameter of a nozzle isabout 18 um, when the Ohnesorge number Oh of the ink 450 is less thanabout 1, the maximum viscosity that is dischargeable at about 3 pL maybe calculated to be about 25 centipoise (cP).

According to some exemplary embodiments, the viscosity of the ink 450containing an organic material may be less than or equal to about 25 cP.As the ink 450 containing an organic material has viscosity of less thanor equal to about 25 cP, the ink 450 may be discharged under about 3 pL,and thus a high resolution display device may be produced. However, toinduce the maximum viscosity that is dischargeable at about 3 pL, it isassumed that the density of the ink containing an organic material isabout 0.99 g/cm³, surface tension is about 34.5 mN/m, and the diameterof a nozzle is about 18 um, but the exemplary embodiments are notlimited thereto. In some exemplary embodiments, the surface tension ofthe ink used for an inkjet printing process may be about 20 mN/m toabout 50 mN/m, and the diameter of a nozzle may be about 10 um to about30 um. For example, as the density, the surface tension, and thediameter of a nozzle of the ink containing an organic material may bevariously changed, the maximum viscosity that is dischargeable at about3 pL, which is about 25 cP, may be changed as well.

FIG. 9 is a graphical depiction of some comparative and exemplaryembodiments comparing viscosity with concentration of ink for eachmolecular weight. FIG. 10 is a graphical depiction of some exemplaryembodiments comparing molecular weight versus concentration when theviscosity of ink is less than or equal to about 25 cP according toprinciples of the invention.

In detail, in FIG. 9 , the curve “a” indicates viscosity versusconcentration when the molecular weight of the organic materialcontained in the ink is 180,000, the curve “b” indicates viscosityversus concentration when the molecular weight of the organic materialcontained in the ink is 30,000, and the curve “c” indicates viscosityversus concentration when the molecular weight of the organic materialcontained in the ink is 2,000. In FIG. 10 , the graph indicates theconcentration according to the viscosity versus the molecular weight andthe relation between the concentration and the molecular weight in whichthe viscosity of ink is less than or equal to 25 cP in the viscositygraph according to concentration for each molecular weight FIG. 9 . Inthis state, FIGS. 9 and 10 , respectively show a graph indicating theviscosity versus concentration of ink for each molecular weight at atemperature of 15° C. to 50° C., and a graph indicating theconcentration according to the viscosity versus molecular weight todeduce the relation between the molecular weight and the concentrationin which the viscosity of the ink is less than or equal to 25 cP.

Referring to FIGS. 9 and 10 , as the maximum viscosity that isdischargeable at 3 pL is 25 cP, assuming that, when the viscosity is 25cP, a coordinate of the curve “a” is P₁, a coordinate of the curve “b”is P₂, and a coordinate of the curve “c” is P₃, the coordinate of P₁ is(3.02, 25), the coordinate of P₂ is (9.32, 25), and the coordinate of P₃is (18.85, 25). Accordingly, when the viscosity is 25 cP, theconcentration for each molecular weight may be 3.02 wt % when themolecular weight is 180,000, 9.32 wt % when the molecular weight is30,000, and 18.85 wt % when the molecular weight is 2,000.

To deduce the relation between the molecular weight and theconcentration, a graph of the viscosity according to the concentrationmay be converted to a graph of the concentration according to themolecular weight as shown in FIG. 10 , by using a value deduced throughthe graph of FIG. 9 . For example, P₁′, P₂′, and P₃′ of FIG. 10 mayrespectively correspond to P₁, P₂, and P₃ of FIG. 9 . When the molecularweight is 180,000, the concentration is 3.02 wt %, and thus thecoordinate of P1′ is (180000, 3.02), when the molecular weight is30,000, the concentration is 9.32 wt %, and thus the coordinate of P2′is (30000, 9.32), and when the molecular weight is 2,000, theconcentration is 18.85 wt %, and thus the coordinate of P3′ is (2000,18.85).

Mathematical Formula 2 below may be deduced by using the coordinate ofP1′, the coordinate of P₂′, and the coordinate of P₃′ that arecalculated as above.y=−3.518*ln(x)+45.59  Mathematical Formula 2

In Mathematical Formula 2, y denotes the concentration of alight-emitting material contained in the ink, and x denotes themolecular weight of the light-emitting material contained in the ink.Furthermore, a coefficient of determination R² of Mathematical Formula 2may be 0.9851.

Furthermore, to produce a display device 1 having a high resolution, theviscosity of the ink 450 containing an organic material may be less thanor equal to 25 cP at a temperature of 15° C. to 50° C., and thus themolecular weight and the concentration of the ink may be expressed as inMathematical Formula 3 below.y>−3.518*ln(x)+45.59  Mathematical Formula 3

In Mathematical Formula 3, y denotes the concentration of alight-emitting material contained in the ink, and x denotes themolecular weight of the light-emitting material contained in the ink.

Accordingly, when the molecular weight of the ink 450 is greater than500, and the viscosity and molecular weight of the ink satisfyMathematical Formula 3, the amount of the ink 450 discharged in theinkjet printing process may be reduced, and thus a high resolutiondisplay device may be produced.

Referring back to FIG. 8 , after the step of forming of the intermediatelayer 220 by discharging the ink 450 including a light-emitting materialonto the pixel electrode 210, the step of forming of the oppositeelectrode 230 on the intermediate layer 220 may be performed.

The opposite electrode 230 may be formed on the intermediate layer 220in a manner covering substantially the entirety of the intermediatelayer 220 and the bank layer 180. The opposite electrode 230 may beformed integrally in substantially the entirety of a display area tocover a plurality of pixels disposed in the display area.

The OLED may be covered by the thin film encapsulation layer. The thinfilm encapsulation layer may include at least one inorganicencapsulation layer and at least one organic encapsulation layer. Inanother exemplary embodiment, the OLED may be covered by theencapsulation plate.

According to some exemplary embodiments, as the organic materialincluded in the intermediate layer 220 has a molecular weight greaterthan about 500, during heating, contamination of adjacent pixels may besubstantially reduced of prevented.

Furthermore, when the concentration and the molecular weight of the inkcontaining an organic material satisfy Mathematical Formula 3, theamount of the ink discharged in the inkjet printing process may bereduced so that a high resolution display device may be produced.

Display devices constructed according to the principles of and exemplaryimplementations of the invention and in exemplary methods ofmanufacturing display devices according to the principles of theinvention as the upper surface or lateral surface of the bank layer 180has liquid repellency, coating of the non-display area with the inkcontaining an organic material may be prevented or reduced. Furthermore,as intermediate layer 220 is formed through the inkjet printing process,the efficiency of the display device manufacturing process may beimproved. According to some exemplary embodiments, as the concentrationof ink and the molecular weight of the organic material are deducedthrough a correlation between the viscosity of ink, the concentration ofink, and the molecular weight of the organic material contained in theink, the reliability of the display device may be improved.

Although certain exemplary embodiments and implementations have beendescribed herein, other embodiments and modifications will be apparentfrom this description. Accordingly, the inventive concepts are notlimited to such embodiments, but rather to the broader scope of theappended claims and various obvious modifications and equivalentarrangements as would be apparent to a person of ordinary skill in theart.

What is claimed is:
 1. A method of manufacturing a display device, themethod comprising the steps of: forming a pixel electrode on asubstrate; forming a bank layer on the pixel electrode, the bank layerhaving an opening exposing at least part of the pixel electrode; andforming an intermediate layer on the pixel electrode by discharging inkcomprising an organic material onto the pixel electrode, wherein theorganic material has a molecular weight greater than about 500 and lessthan about 1,000,000 g/mol, and the organic material in the ink has aconcentration and the molecular weight of the organic material satisfy:y>−3.518*ln(x)+45.59, wherein y is the concentration of the organicmaterial, and x is the molecular weight of the organic material.
 2. Themethod of claim 1, wherein the molecular weight of the organic materialis greater than about 500 and less than about 400,000.
 3. The method ofclaim 1, wherein the ink has an Ohnesorge number of less than about 1.4. The method of claim 1, wherein viscosity of the ink is less than orequal to about 25 cP.
 5. The method of claim 1, wherein the step offorming the bank layer comprises: forming a photoresist layer on thepixel electrode; exposing at least part of the photoresist layer; andforming the bank layer by at least partially exposing the photoresistlayer.
 6. The method of claim 5, wherein the opening of the bank layeris formed by developing the photoresist layer.
 7. The method of claim 6,wherein the intermediate layer is disposed in the opening of the banklayer.
 8. The method of claim 5, further comprising, after the formingof the bank layer, the step of heating the bank layer.
 9. The method ofclaim 8, wherein an upper surface of the bank layer has liquidrepellency.
 10. The method of claim 8, wherein an upper surface and alateral surface of the bank layer have liquid repellency.
 11. The methodof claim 8, wherein the bank layer comprises a fluorine resin.
 12. Themethod of claim 5, wherein the bank layer comprises a negativephotoresist.
 13. The method of claim 1, further comprising, after theforming of the intermediate layer, the step of forming an oppositeelectrode on the intermediate layer.
 14. The method of claim 13, whereinthe opposite electrode covers the intermediate layer and the bank layer.